Apparatus for vacuum deposition of metals



March 13, 1962 N. MILLERON 3,024,965

APPARATUS FOR VACUUM DEPOSITION OF METALS Filed Oct. 8, 1957 3Sheets-Sheet 1 WATER SUPPLY 5O INVENTOR.

NORMAN MILL ERON ATTORNEX POWER SUPPLY March 13, 1962 Filed Oct. 8, 1957N. MILLERON APPARATUS FOR VACUUM DEPOSITION OF METALS 3 Sheets-Sheet 2D.C. POWER SUPPLY SUPPLY INVENTOR. 3/ NORMAN M/LLERON BY 5 ,(4 WWATTORNEY.

March 13, 1962 N. MILLERON 3,024,965

APPARATUS FOR VACUUM DEPOSITION OF METALS Filed Oct. 8, 1957 3Sheets-Sheet 3 POWER I03 SUPPLY INVENTOR. NORMAN M/LLERON BY ATTORNEY.

charge of the electron gun.

Unite This invention relates in general to the vacuum deposition ofmetals, and particularly to an apparatus and process for the vacuumdeposition of metals wherein the deposition is continuous. The inventionmay be specifically applied wherever a metal coating is desired, andbecause of the continuous deposition of metal characteristic of theinvention there are particular advantages to be gained when used in highvacuum pumping equipment, including such embodiments as gettering pumpsand ion pumps, in a manner which will be explained in detail. With minorstructural modifications and a different operational procedure thevacuum apparatus is additionally adaptable to a high current electronsource.

In the past the vaporization of metals for the purpose of plating orcoating the metal upon a metallic surface has been largely confined tobatch or intermittent operations. Usually a grounded strip of thedesired plating metal is vaporized by bombarding the strip with anelectron beam supplied by an electron gun. The strip is heated by virtueof the electron current and subsequently melts and vaporizes. Thevaporized metal then radiates radially outward toward the metallicsurface to be coated, which surface is frequently cooled to ensureattachment of the metal film. The entire operation is carried out in aclosed vessel and a fore pump is commonly used to reduce the partialatmospheric pressure within the vessel to the order of lmm. Hg in orderto avoid direct dis- Many different structural embodiments have beenpreviously utilized to accomplish the foregoing. However, in all suchembodiments the metal to be vaporized is either held within a refractorysupporting piece or is self-supported, in which latter case thebombardment is intermittent. When self-supported, the metal to bebombarded is generally a Wire or ribbon which is automatically fed intothe electron gun for bombrardment from a separate chamber. The metal isbombarded until such time as it begins to melt severely and ceases tosupport itself resulting in attendant dripping or clogging of themechanism. The bombardment must consequently be stopped until thetemperature of the wire is reduced to a point where the operation may beresumed.

In the refractory supporting method of the prior art the duration of thecoating operation is dependent upon the amount of metal which can beheld in a refractory or metal container and upon the temperature atwhich severe chemical reaction or melting of the container materialtranspires. In addition, the process cannot be used where extremely purecoatings are desired since the retlractory supporting material tends todiffuse into the coating metal and is radiated with same. The metal filmbeing deposited also becomes contaminated with the entrapped gases heldin the refractory material. Consequently, vapor coating with highlychemically reactive, or refractory, pure metal is not feasible and themethod is furthermore relatively rigid and unadaptable. A process forcontinuously coating over an extended period has heretofore beenimpossible to attain.

A novel apparatus and method for vapor plating metals continuouslywithout contamination from entrapped gases or other sources has now beendiscovered which accord- States Patent ice ingly overcomes theabove-noted inadequacies of the prior art. A suitable plating wire orstrip is fed through an externally cooled feeder tube adapted tothermally, or electrically, shield the wire or strip, the tube beingconstructed of a material having a high enough coefiicient of thermalconductivity that heat contained or generated in the tube surfaces isremoved. Upon emerging from the tip of the cooled tube the wire issubjected to electron beam bombardment or other heating means causingthe wire outside the feeder tube to be heated and to melt. The emergingWire is preferably disposed in a vertical position to ensure symmetricaldistribution of metal by gravitational force and is further disposedgenerally perpendicular to the plane of the electron gun or heat sourcein order to facilitate melting primarily in the outermost tip of thewire. The molten metal tends to form a molten ball held together bysurface forces (i.e., surface tension), when the coolant, wire feed, andheating means are properly regulated. Heat contained in the wire behindthe molten ball is conducted to the feeder tip or tube primarily byradiation rather than conduction. The molten metal in the ball beingevaporated is radiated outward, while additional metal from the feederwire melts. The wire may be continuously degassed prior to introductioninto the feeder tube if pure coatings are desired. Close tolerancebetween the wire and tube is necessary if vacuum integrity is to bemaintained.

The subject invention is accordingly useful in vaporizing pure metals,particularly in instances where continuous vaporization is desired,e.g., in the vacuum plating of metals, as mentioned hereinbefore, toobtain a metallic coat exhibiting corrosion resistance, decorativeeffect, specific surface characteristics, etc. The invention hasadditional, equally important applications in the high vacuum pumpingart where a metal having the characteristic of being able to chemicallyor physically absorb large volumes of gases is required to continuouslyvaporize and coat surfaces to entrap gaseous molecules thereon. A simpleapplication is a gettering pump in which the gettering or gaseousadsorption action of the continuous application of a metal coat is usedto create a very high vacuum, usually after the vacuum cavity hasinitially been evacuated to a pressure of about 10* mm. Hg with a forcepump. During operation, the gaseous particles remaining in the cavityrandomly impinge upon the walls of a container communicably connected tothe cavity being evacuated and are held thereon by the continuouslyincreasing coat of adsorbent metal. A further application of the presentinvention is in ion pumps in which gaseous particles to be evacuatedrandomly enter an area between two cathode plates. A stream of electronspassing between the cathode plates ionizes the gaseous molecules and theresulting ions are attracted to the cathode plates. Ordinarily the ionsare free to leave the plates upon contact therewith since they losetheir charge and become neutral molecules. However, by placing thevaporized metal source of the present invention within the line of sightof the collecting surfaces of the cathode plates, during operation thevaporized metal is coated thereon and as the ions become electricallyneutral upon striking the collecting plates, they are adsorbed by thecontinuously deposited metal. A greater pumping volume can thereby beachieved with the improved ion p-ump than could be obtained otherwise.

By the adaptation of the present invention to the vacuum pumping art, asindicated above, vacuum pressures and pumping speeds are attainablewhich were impossible previously. A limiting factor in all large scalevacuum pumps is the use of organic seals, lubricants and other materialsemployed in their construction. Such materials have rather high vaporpressures or slowly decompose such that pressures lower than 10- mm. Hgare extremely difiicult to attain. Under the present invention suitablybaked and degassed gettering metals such as titanium, tantalum,tungsten, molybdenum, zirconium, niobium, rhenium, thorium, and uraniumare used which have negligible vapor pressures, and accordingly vacuumpressures as low or lower than 10- mm. Hg can be attained while pumpingat rates as high as hundreds of thousands of liters per second.

For gettering pumps the actual capacity per unit time or output of agiven vaporized metal source is in large part determined by the surfacearea of the chamber walls that must be coated with metal and the amountof metal deposited per unit time. In principle, the pump relies upon therandom or thermal motion of the gaseous molecules to cause them to enterthe pumping chamber and to strike a wall surface. Once the moleculestrikes a wall surface it has a tendency to stick for a finite period oftime. When the surface consists of an adsorbent metal that is notalready saturated with adsorbed gases, each molecule which strikes isadsorbed. As the adsorbtive capacity is reached, larger and largernumbers of the gaseous molecules will also tend to be desorbed,according to the equilibria for each individual metal employed with aparticular gas. Fresh degassed metal must be deposited upon the wallsurfaces with a frequency which will ensure that the gas molecules willbe adsorbed substantially faster than they are desorbed.

In general with simple gettering pumps A n molecules of the gas to bepumped will impinge upon a square centimeter of wall surface per second,where n is the number of gaseous molecules per cubic centimeter in thespace immediately adjacent the wall surface in question, and E is theroot mean square velocity of the gas molecules. Under nominal pressuresthis will mean about impingements per second per square centimeter.Similar calculations can be carried out for ion pumps, although theabove figure represents about the maximum number of impingements thatcan be adsorbed by any pump employing a single vaporized metal sourcewithout electrical discharge.

In order to ensure that most of the impinging gaseous molecules willstick to the surface an estimated C n5 metal atoms must also strike eachsquare centimeter of surface per second, where C is variously estimatedat from 3 to 10. This means approximately 10 to 10 atoms of getteringmetal must occupy each cubic centimeter adjacent to the wall areas Whilethe gettering pump is operating. Rates of vaporization beyond about 3 1Oatoms per second cannot be achieved because at this point the vaporizingbeam of electrons from the electron gun breaks down into an electricaldischarge, thereby limiting the actual physical volume of a pumpemploying a single vaporizing metal source. In the present model agettering pump using 30 mil molybdenum coating wire and a vaporizingelectron current voltage of 5 kv. attains pumping speeds of 10 litersper second at pressures as low as l0 mm. Hg with a single vaporizedmetal source. Such pressures and volumes are necessary to meet thedemands of modern vacuum work in thermonuclear machines, particlebombardments and other nuclear applications, mass spectroscopy, etc. Itis only with the advent of a truly continuous vaporization source asprovided by the instant invention that these pressures and volumes arepossible.

As a further application of the present invention, the continuouslysupported molten ball thereby provided may be also utilized as a highcurrent density electron source merely by utilizing alternating currentvoltage instead of direct current voltage between the molten ball andthe electron source filament. High currents are derived from the moltenball during the positive excursion of the alternating voltage whileduring the negative excursion thereof the ball is heated and evaporated.Outputs as high as 200-300 amps for a 860-1000 watt input voltage may beobtained from the molten mass because of its high temperature emissioncharacteristics. Ordinary tungsten filaments, operating at lowertemperatures, require 4600 watts or more for the same amperage, and inaddition would be at least 26 in. long and have other disadvantages. Inthe present applications the identical amount of current could beobtained from a molten ball 0.2 in. in diameter. Unlike the regulartungsten filament the molten ball is not subject to poisoning by thesurrounding atmosphere because it is always evaporating slowly. Thevaporizing molten ball also provides its own vacuum, since there is anautomatic gettering action on adjacent surfaces due to adsorption andion burying in the cvaporative coating portion of the voltage cycle.With slight structural additions or modifications, the high currentelectron source may be used as a means for heating metals to a very hightemperature in vacuum, for positive ion space charge neutralization(creation of ionized plasmas), for high current vacuum tubes, or fornumerous other applications where large currents in high vacuum areneeded.

Accordingly, it is an object of this present invention to provide anovel method and apparatus for continuously producing and supporting amolten ball of vaporizing metal.

A further object of this invention is to provide a method and apparatusfor continuously producing a selfsupporting molten ball of vaporizingmetal on the tip of a wire.

Another object of the invention is to provide a novel method andapparatus for continuously vaporizing metals.

A further object of this invention is to provide a novel method andapparatus for the continuous vacuum plating of pure degassed metals.

Another object of this invention is to provide a method and apparatusfor continuously feeding a metal wire or strip into a vacuum tightmetallic vaporization zone without contamination of the resulting moltenmetal through contact with other materials.

Another object of this invention is to provide a water cooled feedmechanism for continuously feeding a degassed metal strip or wire intoan electron gun chamber for electron bombardment where by regulation ofthe coolant, feed rate, and electron current, a molten ball ofvaporizing metal is self-supported on said wire or strip.

A still further object of this invention is to provide a gettering pumpin which the gettering metal is continuously fed into a vaporizationchamber and is therein vaporized.

A still further object of this invention is to provide a gettering pumpin which a wire or strip of gas adsorbing metal is continuously fedthrough a fluid cooled feed mechanism into an electron gun chamber forelectron bombardment where by regulation of the coolant, feed rate, andelectron current a ball of molten vaporizing metal is continuouslyself-supported on said wire or strip.

Another object of this invention is to provide an ion pump in which acathode plate for attracting gaseous ions is continuously coated with alayer of metal.

An additional object of this invention is to provide an ion pump inwhich a metal wire or strip is continuously fed through a fluid cooledfeed mechanism into an electron gun chamber for electron bombardmentwhere by regulation of the coolant, feed rate and electron current aball of molten metal is self-supported on said wire or strip and isvaporized to continuously coat a cathode plate for attracting ions.

One more object of this invention is to provide an apparatus and methodfor producing and discharging a high current of electrons from acontinuously produced and supported molten ball of vaporizing metal.

One final object of this invention is to provide an apparatus andmethod. for..producing and discharging a current of electrons from acontinuously produced and supported molten ball of vaporizing metalwhich creates vacuum conditions by the gettering action of theevaporating metal vapors.

Additional objects and advantages of the present invention will becomeapparent from the ensuing description taken in conjunction with theaccompanying drawings, of which:

FIGURE 1 is a cross sectional elevation view partially in schematic of apreferred embodiment of an apparatus for the vaporization and vacuumdeposition of metals, the apparatus also being adaptable for use as agetters p p;

FIGURE 2 is a longitudinal cross section of the fluid cooled feed unitof FIG. 1;

FIGURE 3 is a partially schematic cross sectional view illustrating theinvention as embodied in an improved ion pump having apparatus for thecontinuous vaporization and plating of metals upon the cathode plates;and

FIGURE 4 is a cross section of an alternate embodiment of the inventionfor producing and discharging a current of electrons from a continuouslyproduced and supported molten ball of vaporizing metal.

Referring now to FIG. 1, there is shown a preferred embodiment of theinvention which is adapted for emment as a gettering pump and which isprovided with a generally elongated cylinder 11 defining a vacuumchamber 12 opening at the upper end into a vacuum tank (not shown)formed by walls 13. The bottom of chamber 12 is closed by removable baseplate 14 which also serves as an end wall to a second vacuum chamber 16defined by cylinder 17. A pressure fit is provided between cylinders 11,and 17 as by means of bolts 18 acting upon flanges 19, and 21 of suchcylinders 11, and 17, respectively, upon either side of base plate 14and upon deformable metal gaskets 22 interposed therebetween. The secondchamber 16 is suitably closed at the lower end by a removable backingplate 23, and is preferably connected with a fore pump 24 through exitpipe 26.

A vertically disposed water cooled feed unit,27 is coaxially mountedwithin chamber 12 as by threadable engagement with base plate 14. Thefeed unit 27 is shown in cross section in FIG. 2 and consists of athreaded massive plug member 28 adapted to engage base plate 14 andthrough which member extends a bore 29 generally perpendicular to theplane of the exterior threads. A central elongated metal feed tube 31 inclose fitting relation to bore 29 extends the length thereof and for adistance into vacuum chamber 12. Suitable tubes 32 and 33 arerespectively disposed outwardly concentric with respect to feed tube 31each being countersunk for a distance into the top of plug member 28,which provides support therefor, outermost tube 33 being countersunk toa lesser depth than intermediate tube 32. Inlet and outlet ports 34- and36 below base plate 14 in plug member 28 provide coolant entrance andexit means into tubes 32 and 33, respectively. A suitably shaped tip 37is joined to outer tube 33 as shown generally at 38 by any appropriatemeans of rigid. attachment and extends the tube structure to form aunion with feed wire tube 31. Coolant water or equivalent cooling fluidintroduced to inlet port 34 flows upward between tubes 32 and 33, isdeflected by tip 37 and flows downward between tubes 32 and 31 and outexit port 36. Pipes 39 and 41 (see FIG. 1) are preferably connected toexit and inlet ports 36 and 34 respectively and led exteriorly throughchamber wall 17 as shown generally at 4-2 and 53, respectively, tofacilitate connection to an external water supply 4-4.

A feed wire 46 (FIG. 1) fabricated from any desired metal to bedeposited, and wound on a rotatable metal spool 47, passes betweenconventional externally powered feeder rollers 48 and 19 to facilitatecontinuous introduction of the feed wire into feed wire tube 31.

While numerous conventional means may be used to maintain the vacuumaround rotatable drive shafts 57 and 58 extending through wall 17 forconnection to rollers 48 and 49, respectively, the use of liquid metalseals has been found particularly convenient and leak proof; forexample, a metal having a composition of 62.5% gallium, 21.5% indium,and 16% tin, and which melts at approximately 10 C., has been utilizedto great advantage in practice.

Reasonable vacuum integrity is maintained between vacuum chambers 12 and16 communicably connected through feed. wire tube 31 by incorporation ofa feed wire size having a tolerance of 5 mils or less with respect tothe feed Wire tube 31. Degassing of the wire 46 prior to feeding intothe water cooled feed unit 27 is accomplished, as by resistance heatingby means of a conductor 50 connected to a power supply 51 and ledthrough backing plate 23 at a vacuum insulated point 52 to be connectedto a spool holder 53 for supporting spool 47. Holder 53 is made of aconducting metal and is insulated from the backing plate as showngenerally at 54. Power supply 51 is grounded to the backing plate bycontact wire 56 to complete a circuit to ground through a currentconduction path including wire 46. The wire is thus resistance heated byvirtue of the current flowing therethrough. It will be appreciated feedwire 46 may be of any composition depending upon its purpose. Foradsorption and pumping purposes highly adsorptive metals, i.e.,particularly titanium, tantalum, tungsten and molybdenum, as well aszirconium, niobium, rhenium, thorium and uranium, have been foundsuperior.

In order to heat the feed wire 46 emerging from the tip end of feed tube31 to a high temperature, means are provided for bombarding the emergingfeed wire with an electron beam. The means may be provided, for example,in the form of an electron gun 59 having a heated cathode filament 66mounted above tip 37 as by means of cathode posts 61 embedded in andinsulated from base plate 14. Energization of filament 59 to supplyelectrons is facilitated by conductors 62 connected to posts 61 at theunder side of base plate 14. Such conductors lead through insulatedhermetically sealed bushings 63 mounted in backing plate 23 forconnection to a suitable D.C. power supply 64 operating above groundpotential. The electrons emitted by filament 60 are roughly focused ontothe molten ball 72 by a bias screen 66 supported coaxially about tip 37by electrically conducting supports 67 attached to posts 61. Screen 66is thereby maintained at least as negative as the potential of powersupply 64 and therefore of filament 64). Moreover, feed wire 46 isgrounded through base plate 14 as shown gen erally at 68 whereby thepotential gradient thus established between filament 6t) and theemerging tip of feed wire 46 is effective in accelerating the beam ofelectrons thereto. The impinging electron beam vaporizes the tip of feedwire 46 as hereinafter described. with respect to the operation of theinvention. To prevent the metal vapors thus evolved from contaminatingvacuum areas outside of the main pumping cavity 12 a circular plate 69is best disposed in spaced relation to wall 13 by means of supports 71anchored thereto.

The process or method of operation is as follows: The vaporizationchamber 12 is first pumped down by conventional means such as a forepump (not shown) to a pressure of 18 mm. Hg or less to avoid directdischarge when the electron gun 59 is energized. The cooling water isnext circulated through feed unit 27, water of room temperature or evenhigher being suflicient as long as the flow within chamber 12 issufficient to remove heat rapidly. Feeder rollers 48 and 49 are startedand filament 60 is energized. Once the filament 60 has been energizedthe stream of electrons arriving at the emerging feed wire 46 heat thetip of the wire and cause it to become molten. A self-supported moltenball 72 forms at the tip of the wire, which ball is held together bysurface tension. The molten ball 72 shields the feeder tip 37 fromelectron bombardment. Sufiicient energy is rained (concentrated) on thesurface of the molten ball 72 to cause it to evaporate at a rate that ismatched by the rate of feed of the wire. The feed wire immediatelybehind the ball is thermally and electrically protected by the watercooled tip 37 without which the ball 72 has a strong tendency to burnoff because the wire becomes thin and is unable to support the moltenball.

When the vaporization apparatus of the present invention is operatedmerely as a means of vapor coating objects with a metal, suchvaporization apparatus may be modified or simplified as desired toadditionally include means for supporting the objects to be coatedwithin the chamber in receiving relationship to the vaporized metalevolved from molten ball 72. The pumping means 24 for evacuating vacuumchamber 16 and the means for resistance heating of the feed wire 46 arenecessary to hold air and adsorbed vapors to a minimum when extremelypure coatings are desired, e.g., coatings on foils for nuclearbombardments and other nuclear energy applications.

Operation as a pumping means at extremely low pressures, i.e., below 10*mm. Hg, is accomplished by first pumping out the upper and lower vacuumchambers 12 and 16 for extensive periods of time at pressures of mm. Hgor less to degass the gases normally entrapped on the walls thereof.During this preliminary pumping period, or during later operation, powersupply 51 provides means for heating the feed wire 46 to a temperatureof the order of 2000 C. by resistance heating, the exact temperaturedepending upon the melting point of the particular wire material beingused. All gaseous impurities are normally degassed at this temperatureand the feed wire 46 than has a purity commensurate with that of theoriginal metal. The entire vaporization unit is next brought intooperation as detailed previously and vaporized metal continuouslytravels in a line of sight from the molten ball to the walls and anyother surfaces disposed within the chamber 12. The clean pure metalcoats the walls continuously and adsorbs and covers gaseous moleculesthereon by chemisorption and physical adsorption mechanisms. Withradiation rates of the order indicated above and with cylindrical pumpshaving on the order of 10 square centimeters wall area, pumping rates ashigh as 10 l./sec. may be obtained at 10* mm. Hg. These quantitiesoperate as an upper limit for a single vaporization unit, althoughseveral such units may be arranged within the same pump housing toincrease the pumping action.

While the pumping capacity as developed above is related to pumpinternal surface area and volume of vaporized metal radiated per unittime from feed unit 27, there must be sufiiciently large passagewaysinto the gettering cavity 12 from the vessel to be evacuated for largenumbers of gaseous molecules to enter because of their random or thermalmotion. During deposition, the metal coat builds up in an irregularmanner with many ridges and valleys caused by initial uneven depositionto thus increase the effective collecting surface area.

The gettering or vaporizing metal source of the present invention, viz.,feed unit 27, may be additionally employed as a continuous getteringsource in an ion pump, as shown in FIG. 3, to enhance the pumping actionthereof. More particularly, there is provided a vacuum cavity 73 definedby container walls 74 connected to a cavity to be evacuated (not shown)through passageway 76 defined by an inlet conduit 77. Disposed withinthe cavity 73 in generally opposing positions and preferably on eitherside of passageway 76 are a pair of cathode electrodes 78. Theelectrodes 73 are insulated from wall 74 and energized with alternatingvoltage supplied by means of leads 79 connected to a tap of an AC. powersupply 81. A magnetic field having a direction as indicated by arrow 82normal to the cathode surfaces is created between the two electrodes 78by a magnet (not shown) exterior to the wall 74. Two grids 83,respectively located proximate the facing sides of electrodes 82, areinsulated therefrom and operated at a slightly higher alternatingpotential than the electrodes 78 by connection with a suitable tap ofpower supply 81 as by means of leads 84. A filament 86 is spaced betweenone of the grids 83 and corresponding electrodes 78 and is connected bymeans of insulated wire $57 to an appropriate tap of power supply 81 foroperating the filament at a potential intermediate the potentials of thegrids and electrodes. The chamber wall 74- operates at ground potentialas indicated at 88.

All of the foregoing elements are conventional in various known ionpumps and are presented herein merely for purposes of illustration. Insuch conventional ion pumps an electron stream emitted from filament 86oscillates between electrodes 7h due to the action of magnetic field 82and the alternating electric field established by the potentials appliedto electrodes 78 and grids 83. The oscillating electron stream ionizesgas molecules entering cavity 73 by random motion from a vessel to beevacuated. The ions thus produced are attracted to electrodes 78 andcollected thereon to produce a pumping action. The ions upon impingingupon the electrodes, however, are neutralized and are free to migrateaway from the plates. The accumulation of neutral molecules so formed inthe region of electrodes 78 are then commonly evacuated by means of amechanical vacuum pump (not shown).

In accordance with the salient features of the present invention, thepumping capacity of a conventional ion pump, for example of the typedescribed above, is materially increased by the incorporation therein ofa water cooled feed unit 27 as previously described. Such feed unit 27is best disposed with the water cooled tip 37 thereof in a verticalposition within ion pump cavity 73. The molten ball 72, when formed bythe feed unit, is preferably in a line-of-sight distance from all partsof the opposing surfaces of electrodes 78. The electron source and otheraccessory means of the metal vaporizing source of the instant invention(not shown in detail in FIG. 3) may be the same as those shown in thegettering pump of FIG. 1, or may vary structurally as long as the samefunction (namely, production of a bombarding electron beam) isperformed.

The process of operation is as follows: The vacuum cavity 73 andchambers to be evacuated are first pumped down to a pressure of theorder of 10" mm. Hg as by means of a standard fore pump 89 connected topassage 76 by piping M. The components of the vacuum feed unit 27 aresimilarly pumped down and degassed, as in the gettering pump embodimentof FIG. 1 previously described. Operation of the metal vaporizationmeans in the manner hereinbefore described provides a continuous streamof metal vapors which travel in a line of sight radially away from themolten ball 72 formed by feed unit 27. Electrodes 78, not yet energized,are continuously coated with metal vaporized from molten ball 72, and agettering action is thus provided which traps a portion of the gaseousmolecules entering cavity 73 through passageway 76 upon all surfaceswhere the metal coats. Upon activation of power supply 81 an oscillatingelectron stream is established in cavity 73 which then ionizes gaseousmolecules in the conventional ion pumping manner, the ions beingattracted to electrodes 78 and neutralized thereat. The neutral gasmolecules which are commonw 1y free to migrate away from the electrodesare now trapped upon such electrodes by virtue of the concurrentlydeposited adsorptive metallic molecules emanating from feed unit 27which establish a matrix for chemically inert gas molecules shot intothe electrodes by the action of the electric field. The acceleration ofions caused by the potential dilferential between grids 83 andelectrodes 78 causes the gaseous and metal ions to both stick verytightly to the electrodes. The gettering action produced by the presentinvention thus eifectively increases the pumpmg capacity of the ion pumpby holding the gaseous particles onto the ion pump electrodes 78.

Operation of the present inventive structure as a means for maintaininga vacuum while at the same time acting as a source of a high current ofelectrons is illustrated in the embodiment of FIG. 4 where there isshown a vacuum cavity 92 defined by walls 93. A water cooled feed unit27, similar in structure and design to the mechanism of the same numberin FIGS. 1 and 2, is disposed vertically through the top wall 94 ofcavity 92 together with feed Wire and Wire feed mechanism, coolant andcoolant feed means, secondary vacuum pumping means and other componentsof the metal vaporization apparatus described in connection with FIGS. 1and 2 and accordingly not shown in detail in the present figure. Acathode filament 96 is disposed beneath the feed unit 27 and ismaintained at a higher potential than the electrically grounded feedunit 27 by connection to an A.C. power supply 97 through insulated leadwires 98. An extraction grid 99 may in addition be optionally disposedbetween the molten ball 72 formed by feed unit 27 and the filament 96,in which case the grid is connected through insulated conductor 1% to atap of power supply 97 for producing a voltage of the same phase asapplied to filament 96 but of smaller amplitude. The grid serves tolessen the distance between the two conductors and thereby increases thetransmission amperage of the electron stream originating at filament 96.

A metallic collector block 101 to be heated or melted is disposedbeneath the filament 96 and is maintained at a higher potential than thefilament by means of an insulated lead wire 102 connecting the block 101with a suitable tap of AC. power supply 97. Obviously other receivingmeans may be substituted for the block 101 when the high densityelectron current is to be used for other purposes. A pump 103 connectedto the vacuum cavity 92 by outlet 164 is used to pre-evacuate the cavityto a pressure of about mm. Hg.

With the cavity 92 pre-evacuated and feed unit 27 together with itsaccessory equipment degassed as previously described in relation to theembodiment of FIGS. 1 and 2, the feed unit and accessories are nextplaced into operation and AC. power supply 97 energized. Initially astream of electrons is produced by filament 96 and the electrons arealternated between the feed wire tip and plate 101 due to thealternating electric field established therebetween with the frequencyof alternation being determined by the frequency of output voltagesupplied by power supply 97. The alternating electron stream is initially of small amperage. As the feed wire heats up due to bombardmentby the electrons and forms molten ball 72, however the electronconstituent of the vaporized metal emanating from the ball is extractedduring the positive alternations of the applied electric field andattracted toward plate 191 to materially increase the amperage of thealternating electron stream. During the negative alternations of theapplied field, the electrons (including both the electrons emitted byfilament 96 as well as a portion of the electrons previously extractedfrom the vaporized metal) are attracted to molten ball 72 formed at feedunit 27 resulting in the continued heating and evaporation of the ballby electron bombardment. It is to be appreciated that in the presentembodiment, the molten ball 72 not only functions to produce an intenseelectron stream but in addition the process of vaporization keeps themolten ball emitter free from contamination and the coating formedeifectively adsorbs substantially all gaseous particles in cavity 92 toproduce an extremely high vacuum therein.

While the invention has been disclosed with respect to but severalpreferred embodiments, it will be apparent to those skilled in the artthat numerous variations and modifications may be made Within the spiritand scope of the invention and thus it is not intended to limit theinvention except as defined in the following claims.

What is claimed is:

1. In an apparatus for continuous deposition of metal vapors, thecombination comprising a metal feed wire of vapor plating material, acooled feed wire tube disposed coaxially about said feed wire in closetolerance therewith and terminating at the feed end in a generallyvertical position to maintain the wire in a vertical position as itemerges from said tube, means coupled to said feed wire for continuouslyfeeding same through said tube at a uniform rate, and means for rapidlyheating said wire emerging from said tube to form from said wire a ballof molten metal self-supported on the emerging end thereof whereby saidwire is continuously heated to form said molten ball and said moltenball is continuously vaporized.

2. In an apparatus for the continuous vacuum deposition of metal, thecombination comprising a vacuum tight container, means coupled to saidcontainer for initially evacuating same to a pressure of at least about10* mm. Hg, a coolant-jacketed feed wire tube disposed to terminate atthe feed end in a generally vertical position within said container todischarge feed wire in a vertical position, a metal wire of materialsuitable for vapor plating extending through said tube, means coupled tosaid wire for continuously feeding the wire through said tube at auniform rate, an electron source carried by said container and disposedto produce an electron beam for bombarding the tip of the wire emergingfrom said tube, and a ball of molten vaporizing metal formed from andself-supported on the end of said emerging wire, whereby said wire iscontinuously heated to form said molten ball and said ball iscontinuously vaporized.

3. Apparatus as defined by claim 2 further defined by saidcoolant-jacketed feed wire tube comprising a central elongated metallictube having a bore diameter for establishing a close fittingrelationship with respect to the feed wire, an outer metallic tubedisposed concentrically about said central tube, an intermediatemetallic tube concentrically interposed between said outer and centraltubes and terminating at an axial position rearwardly from one end ofsaid central tube, a metallic tip extending between the opposite end ofsaid central tube and the corresponding end of said outer tube, meansattached between said outer and intermediate tubes at the distal endsthereof with respect to said tip for terminally closing the interveningspace between said outer and intermediate tubes, structure defining aninlet port communicating with said intervening space between said outerand intermediate tubes at said distal end thereof with respect to saidtip to admit coolant thereinto, and structure defining an outlet portcommunicating with the intervening space be tween said intermediate andcentral tubes at said distal end thereof with respect to said tip forremoving coolant therefrom.

4. In an apparatus for the continuous'vacuum deposition of metal, thecombination comprising a vacuum-tight container, means communicablyconnected to said container for initially evacuating same to standardfore vac dimensions, a vertically disposed jacketed feed wire tubecommunicating through one wall of said container, means connected tosaid tube for circulating coolant through the jacket thereof, arotatably supported spool, metal feed wire wound upon said spool andextending through said feed wire tube and emerging in a verticalposition, rotatably driven feeder rollers engaging said wireintermediate said spool and feed tube for continuously feeding said wirethrough said tube at a uniform rate, heat generating means for heatingand degassing said wire prior to entry into said tube, an electronemissive filament internally supported within said container verticallyproximal the end of said feed tube from which said feed wire emerges,and a focusing grid disposed coaxially about the end of said feed tubefor concentrating electrons emitted from said filament upon the tip ofsaid feed wire emerging from said tube, said electrons uniformly heatingthe emerging tip of said feed wire, and a continuously evaporated moltenball self-supported thereon.

5. Apparatus as defined in claim 4 but wherein the feed wire metal isselected from the group consisting of tungsten, tantalum, molybdenum,titanium, zirconium, niobium, rhenium, thorium and uranium to produce agettering action.

6. Apparatus for the continuous vacuum deposition of metal comprising avacuum tight container adapted to stand upright, a second vacuum tightcontainer, a pressure sealed base plate common to said first and secondcontainers, a massive plug member mounted in said base plate and havinga central axial bore communicably connecting said first and secondcontainers, said plug member partially projecting into said secondcontainer, an elongated metal feed tube extend-ing the length of saidbore in close fitting relation therewith and projecting vertically intothe interior of said first container, an outer metal tube disposedoutwardly concentric of said feed tube and countersunk into said plugmember, an intermediate metal tube concentrically interposed betweensaid outer tube and said feed tube, said intermediate tube countersunkinto said plug member to a greater depth than said outer tube andextending to an axial position spaced rearwardly from the projecting endof said feed tube, a metal tip extending from the projecting end of saidouter tube to the corresponding end of said feed tube, an inlet portmounted in the portion of said plug member projecting into said secondcontainer and communicably connected to the intervening space betweensaid outer and intermediate tubes, an outlet port mounted in the portionof said plug member projecting into said second container andcommunicably connected to the intervening space between saidintermediate tube and said feed tube, a coolant supply connected betweensaid inlet and outlet ports for circulating coolant therethrough, aspool rotatably mounted within said second container and electricallyinsulated therefrom, metal feed wire of a material to be vacuumdeposited wound upon said spool and extending through said vertical feedtube in close tolerance therewith, and thereby emerging in a verticalposition, rotatably driven feeder rollers mounted within said secondcontainer and engaging said feed wire intermediate said spool and saidfeed tube for continuously feeding said wire into the feed tube at aconstant rate, means connecting said feed tube to ground, a power supplyconnected between said spool and ground for resistance heating said feedwire, and an electron gun carried by said first container and disposedproximal said tip for electron bombarding in the axial direction thereoffeed wire emerging from said feed tube to uniformly heat and form acontinuously evaporated molten ball from the emerging feed wire andself-supported thereon whereby metallic surfaces to be coated may bedisposed within said first container and the evaporated metalcontinuously deposited thereon.

7. In an apparatus for continuously pumping gases by adsorption ontofreshly deposited metal, the combination comprising a vacuum tightcontainer opening into a cavity to be evacuated, a coolant-jacketed feedWire tube terminating at the feed end in a generally vertical positiondisposed through a wall of said container to discharge feed wire in avertical position, means for connecting the coolant jacket of said feedwire tube with an exterior pressurized coolant supply, a metal wirehaving good gettering properties extending through said tube and inclose tolerance therewith, a second vacuum tight container having saidwall through which said tube is disposed in common with said firstcontainer, means communicating with said vacuum tight container and saidsecond container for evacuating same to a pressure of about mm. Hg, aspool rotatably mounted in said second container and having said wirewound thereon, means carried by said container for continuously feedingsaid wire from said spool through said tube at a uniform rate, heatingmeans carried by said second container for initially heating anddegassing said wire prior to entrance into said tube, an internallysupported electron emission filament in said first container verticallyproximal and perpendicular to the wire emerging from said tube, afocusing grid supported around the emerging tip of said wire, anexterior power source connected in energizing relation to said filament,and a ball of molten vaporizing metal formed from and supported on theemerging tip of said wire, whereby said wire is degassed prior to beingcontinuously heated by electron bombardment to form said molten ball andsaid ball is continuously vaporized and deposited on said vacuum tightcontainer walls to produce a gettering action.

8. In an apparatus for continuously removing ionized gases, thecombination comprising an ion pump including at least one electrode uponwhich ions are collected and neutralized to form gaseous molecules, afeed tube terminating at the feed end in a generally vertical positionand extending interiorly of said pump and adapted for a vertical feedwithin line-of-sight of said electrode, jacket means for cooling saidtube, a gettering wire extending through said tube and emergingtherefrom, means carried by said pump for continuously feeding said wirethrough said tube at a uniform rate, means for rapidly and uniformlyheating said wire emerging from said tube, and a ball of molten metalformed from and self-supported on the end of said emerging wire wherebysaid wire is continuously heated to form said molten ball and said ballis continuously vaporized to deposit said gettering metal upon saidelectrode.

9. In an ion pump in which the metal surfaces of the cathode electrodesare continuously coated with an adsorptive metal, the combinationcomprising a vacuum tight container opening into a cavity to beevacuated, means for initially evacuating said container to a pressureof at least about 10* mm. Hg, means including a pair of spacedcathodeelectrodes carried within the container for ionizing gas enteringsaid container from said cavity, said cathode electrodes collecting andneutralizing ionized gases, a feed wire tube terminating at the feed endin a generally vertical position extending through a wall of saidcontainer and adapted to feed wire vertically within line of sight ofsaid electrodes, means coupled with said tube for cooling same, agettering wire extending through said tube and in close tolerancetherewith and emerging in a vertical position, means engaging said wirefor continuously feeding the wire through said tube at a uniform rate,means disposed within said container for rapidly heating the tip of theWire emerging from said tube, and a ball of molten metal formed from andself-supported on the emerging end of said wire, whereby said wireduring operation of said pump is continuously heated to form said moltenball and said ball is continuously vaporized to deposit said getteringmetal upon said electrodes.

10. An ion pump comprising a vacuum tight container opening into acavity to be evacuated, fore pump means communicating with saidcontainer, means including a pair of spaced electrodes disposed withinsaid container for establishing an oscillating electron dischargebetween said electrodes, said electron discharge ionizing gas enteringsaid container to establish an ionized gaseous discharge between saidelectrodes with the ions being collected and neutralized thereon, ajacketed feed tube mounted in a Wall of said container and having thefeed tip projecting generally vertically and interiorly of saidcontainer in line of sight relationship with said electrodes, coolantmeans connected to said feed tube for circulating coolant through thejacket thereof, a rotatably mounted spool, gettering wire wound uponsaid spool and extending through said feed tube to emerge in a verticalposition, means engaging said wire for continuously feeding same 13through said tube at a uniform rate, an electron gun disposed withinsaid container vertically proximal the tip of said feed tube forbombarding the gettering wire emerging from said tube with electrons,and a continuously evaporated molten ball of gettering wire materialselfsupported on the emerging end of said wire whereby said electrodesduring operation of said pump are continuously coated with the getteringwire material to trap the neutralized ions upon the electrodes byadsorption.

11. In an apparatus for continuously producing a high density electroncurrent in a vacuum, the combination comprising a vacuum tightcontainer, means coupled to said container for initially evacuating sameto a pressure of about mm. Hg, a feed wire tube disposed within saidcontainer to terminate at the feed end in a generally vertical positionand connected to ground, jacket means for cooling said tube, a getteringwire extending through said tube and emerging therefrom, means carriedby said container for continuously feeding said wire through said tubeat a uniform rate, an alternating current electron source deposedproximal and perpendicular to the axis of said wire emerging from saidtube to heat the wire by AC. electron bombardment, a ball of moltenmetal formed from and supported on the end of the emerging wire, andelectron receiving means disposed coaxial with said emerging wire and onthe opposite side of said electron source from said tube, said means inphase with said electron source and of a greater electrical potentialthan said source whereby said molten ball is heated and vaporized by astream of electrons during the negative alternation of said source and ahigh density electron current is discharged to said receiving meansduring the positive alternation of said source.

12. A high current electron source comprising a vacuum tight container,vacuum pump means connected to said container for evacuating same to apressure of about 10' mm. Hg, a jacketed feed tube mounted in a Wall ofsaid container and having a tip projecting interiorly thereof, said tipterminating in a generally vertical position, coolant means connected tosaid feed tube for circulating coolant through the jacket thereof, arotatably mounted spool having gettering wire wound thereon, saidgettering wire extending through said feed tube in close tolerancetherewith and emerging from the tube in a vertical position, feed meansengaging said wire for continuously feeding same through said tube at auniform rate, a filament vertically disposed in coaxial alignment withthe axis of the emerging gettering wire, an extraction grid coaxiallyinterposed between said filament and said emerging wire, electronreceiving means coaxially disposed on the opposite side of said filamentfrom said grid, an AC. power supply coupled to said grid, filament, andreceiving means to apply respective in phase alternating voltages ofincreasing amplitudes thereto, and means connecting said feed tube toground.

13. In a method for the continuous vacuum deposition of metal, the stepscomprising evacuating a vaporization and deposition chamber to apressure of at least about 10' mm. Hg, feeding a metal wire continuouslythrough a coolant-jacketed feed wire tube disposed for vertical wirefeed in said chamber, said wire being in close tolerance with said tube,bombarding the tip of said wire emerging from said tube with a beam ofelectrons, whereby said tip heats and melts, and regulating the wirefeed, coolant feed, and electron beam to cause the formation of moltenvaporizing metal self-supported on said tip by surface tension in whichadditional wire is continuously melted to replace metal lost byvaporization.

14. In a process for the continuous vacuum deposition of a metal, thesteps comprising evacuating a vaporization and deposition chamber to apressure of at least about 16* mm. Hg, continuously evacuating a secondadjacent chamber containing a metal wire on a spool, heating anddegassing said wire, feeding said wire from said spool lid continuouslythrough a coolant jacketed feed wire tube disposed to have said wire ina vertical position in said vaporization chamber as it emerges, saidwire being in close tolerance with said tube, bombarding the tip of saidwire emerging from said tube with a beam of electrons, whereby said tipheats and melts, and regulating the wire feed, coolant feed, andelectron beam intensity to cause formation of a ball of moltenvaporizing metal self-supported on said tip by surface tension in whichadditional wire is continuously melted to replace metal lost byvaporization.

15'. In a process for the continuous adsorption of gases onto freshlydeposited metal, the steps comprising vertically feeding a degassedgettering wire continuously through an exteriorly cooled feed wire tubeinto a vacuum tight container evacuated to a pressure of at least about10 mm. Hg, said container opening into a cavity to be evacuated, heatingthe tip of said wire emerging from said tube, and regulating the wirefeed, coolant feed and electron beam intensity to form a vaporizingmolten ball self-supported on said tip by surface tension whereby saidvaporizing metal coats surface areas within said container to produce agettering action.

16. In a process for the pumping of gases by adsorption onto a getteringmetal continually being deposited on a surface, the steps comprisingevacuating a vacuum tight container to a pressure of at least about 10"mm. Hg, said container opening into a cavity to be evacuated, degassinga gettering wire, feeding said gettering metal wire continuously througha coolant jacketed feed wire tube disposed to maintain said wire in avertical position in said chamber as it emerges, said wire being inclose tolerance with said tube, bombarding the tip of said wire emergingfrom said tube with a beam of electrons to heat and melt said tip, andregulating wire feed, coolant feed, and electron beam intensity to causethe formation of a ball of molten metal self-supported on said tip bysurface tension in which additional wire is continuously melted toreplace metal lost by vaporization, whereby said vaporizing metal coatssurface areas within said container to produce a gettering action.

17. In a process for continually evacuating gases, the steps comprisingoperating an ion pump having a charged cathode electrode to ionize saidgases and collect and neutralize the resulting ions at said electrode,feeding a degassed gettering wire continuously through an exteriorlycooled feed wire tube into said pump within line of sight of saidelectrode, said wire being in close tolerance with said tube, said tubeterminating at the feed end in a generally vertical direction uniformlyheating the tip of said wire emerging from said tube, and regulating thewire feed, coolant feed and electron beam density to form a vaporizingmolten ball self-supported on said tip by surface tension whereby saidvaporizing metal continuously coats said electrode.

18. In a process for continuously evacuating gases, the steps comprisingoperating an ion pump having a charged cathode electrode to ionize saidgases and collect and neutralize the resulting ions at said electrode,degassing a gettering wire, feeding said gettering wire continuouslythrough a coolant jacketed feed wire tube terminating at the feed end ina generally vertical direction being disposed to maintain said wire in avertical position as it emerges in said ion pump within line of sight ofsaid cathode electrode, said wire being in close tolerance with saidtube, bombarding the tip of said wire emerging from said tube with abeam of electrons to heat and melt said tip and regulating wire feed,coolant feed, and electron beam intensity to cause the formation of aball of molten metal self-supported on said tip by surface tension inwhich additional wire is continuously melted to replace metal lost byvaporization and said vaporizing metal coats said cathode electrode toproduce a gettering action.

19. In a process for continuously evacuating gases, the

aeeasee steps comprising operating an ion pump having a charged cathodeelectrode to ionize said gases and collect and neutralize the resultingions at said electrode, continuously evacuating a second adjacentchamber containing a gettering metal wire on a spool, feeding said wirefrom said spool continuously through a coolant jacketed feed wire tubeterminating at the feed end in a generally vertical direction and beingdisposed to maintain said wire in a vertical position as it emerges insaid ion pump within line of sight of said cathode electrode, said wirebeing in close tolerance with said plate, bombarding the tip of saidwire emerging from said tube with a beam of electrons to heat and meltsaid tip, and regulating the wire feed, coolant feed, and electron beamintensity to cause formation of a ball of molten vaporizing metalself-supported on said tip by surface tension in which additional wireis continuously melted to replace metal lost by vaporization, wherebysaid vaporizing metal coats said cathode electrode to produce agettering action.

20. In a process for producing a high density electron current in avacuum, the steps comprising evacuating a vacuum tight container to apressure of at least about mm. Hg, feeding a degassed gettering wirecontinuously through an eXteriorly cooled feed wire tube into saidcontainer, said tube terminating at the feed end in a generally verticaldirection, said wire being in close tolerance with said tube to maintainthe wire in a vertical position as it emerges from said tube, producinga stream of electrons from a source within said container, establishingan alternating electric field between said source and the emerging tipof said wire to alternately focus the electron stream thereon, andregulating the wire feed, coolant feed and electron beam density to forma self-supported evaporating molten ball of the wire material andextract electrons from said ball, and collecting said electrons at areceiver disposed within said electric field whereby a high densityelectron current is emitted from said molten ball.

21. In an apparatus adaptable to the continuous vacuum deposition ofmetals and to the continuous gettering of gases by metals as well as theproduction of high density electron currents in vacuum, the combinationcomprising a vacuum-tight container, means coupled to said container forinitially evacuating same to a pressure of at least about 10" mm. Hg, acoolant-jacketed feed wire tube vertically deposed within saidcontainer, a metal Wire of material suitable for vapor plating andgettering gases extending through said tube, means coupled to said wirefor continuously feeding the Wire through said tube at a uniform rate,an electron source carried by said container in vertical spaced relationto said metal Wire extending through said vertical feeder tube toproduce an electron beam for bombarding said wire emerging from saidtube, and a ball of molten vaporizing metal formed from and selfsupported on the end of said emerging wire, whereby said wire iscontinuously heated to form said molten ball, and said ball iscontinuously vaporized.

22. in an apparatus for continuously pumping gases by adsorption ontofreshly deposited metal, the combination comprising a vacuum tightcontainer opening into a cavity to be evacuated, means communicatingwith said container for initially evacuating said container to apressure of about 10 mm. Hg, a coolant jacketed feed wire tubeterminating in a generally vertically upward position disposed to feedgettering wire into said container, means for connecting the coolantjacket of said feed wire tube with an exterior pressurized coolantsupply, a degassed metal Wire having good gettering properties extendingthrough said tube and in close tolerances therewith, means carried bysaid container for feeding said degassed metal wire continuously throughsaid feed tube from a spool at a uniform rate, an internally supportedelectron source vertically spaced from said discharge end of saidjacketed feeder tube, an exterior power supply connected in energizingrelation with said electron source, whereby during operation said wireis continuously heatedby electron bombardment, and a ball of moltenvaporizing metal formed from and self-supported on the emerging tip ofsaid wire.

References Cited in the file of this patent UNITED STATES PATENTS2,103,623 Kott Dec. 28, 1937 2,293,186 Wydler Aug. 18, 1942 2,469,006Shelby May 3, 1949 2,527,747 Lewis Oct. 31, 1950 2,746,831 Chapman May22, 1956 2,754,259 Robinson et al July 10, 1956 2,825,619 Miller Mar. 4,1958 2,850,225 Herb Sept. 2, 1958 FOREIGN PATENTS 754,102 Great BritainAug. 1, 1956

